Concept

Position sizing isn’t just about how much money you throw at a stock—it’s about how much risk you’re willing to take on per trade. Think of it like filling a glass of water: too much, and it spills; too little, and you’re thirsty. The formula is simple: Position Size = (Account Risk per Trade) / (Trade Risk). Account Risk per Trade is the maximum you’re willing to lose (say, 1% of your portfolio), and Trade Risk is the difference between your entry price and your stop-loss. If you’re buying Safaricom at KES 45 and your stop is at KES 42, your trade risk is 6.67%. If your account risk is KES 10,000, you buy 33 shares. That’s it. No magic, no guesswork—just math.

This isn’t about predicting winners. It’s about surviving long enough to let your winners run. Position sizing is the difference between a trader who blows up their account in three months and one who compounds wealth over years. It measures your discipline, not your luck. It doesn’t care if you’re right or wrong—only that you live to fight another day.

Here’s the kicker: position sizing works best when the market is volatile. In calm markets, your stops might get hit too often, eating into profits. But in a crash? It’s your seatbelt. It’s the reason some investors survived the 2020 COVID sell-off while others got wiped out. The key is consistency—applying the same rules whether the NSE is up 2% or down 5%.

NSE Context

On the Nairobi Securities Exchange, position sizing isn’t just a nice-to-have—it’s a survival tool. The market is small, concentrated (hello, Safaricom and KCB), and liquidity dries up faster than a mama mboga’s stall at 6 PM. If you size your positions like you’re trading Apple on the NYSE, you’ll get wrecked. Here’s why:

First, liquidity constraints mean slippage is real. A KES 100,000 order in a KES 50 million daily turnover stock moves the price. Second, the market’s love for dividends means investors often hold stocks for income, not growth—so your stop-loss might get triggered by a routine dividend drop, not a real sell-off. Third, sector concentration (financials and telecoms make up over 60% of the NSE 20) means a single bad bet in KCB or Safaricom can wipe out a diversified portfolio.

Take AIB for example. In 2025, the stock swung between KES 32 and KES 41. An investor who sized their position to risk 1% of their portfolio per trade would have bought 250 shares at KES 35 with a stop at KES 32. If the trade went wrong, they lost KES 750—barely a blip. But if they’d gone all-in like it was a sure thing? A 20% drop would’ve erased KES 2,000. The concept would’ve told them to cut losses early and live to trade another day.

Practical Example

Let’s say you’re eyeing Centum at KES 18.50. You’ve done your homework: the company’s land portfolio is undervalued, and the dividend yield is juicy. But here’s the thing—Centum’s stock can swing 10% in a week based on nothing. So how much do you buy?

Step 1: Define your risk. Let’s say you’re willing to lose 1% of your KES 500,000 portfolio on this trade. That’s KES 5,000.

Step 2: Set your stop-loss. You decide a 7% drop from KES 18.50 is your cut-off. That’s KES 17.21.

Step 3: Calculate trade risk. (18.50 - 17.21) / 18.50 = 6.97%.

Step 4: Position size. KES 5,000 / 6.97% = KES 71,736. At KES 18.50, that’s 3,878 shares.

Now, what does this tell you? If Centum drops to KES 17.21, you lose KES 5,000—your pre-defined risk. If it rises to KES 22, your profit is (22 - 18.50) * 3,878 = KES 13,573. That’s a 2.7x return on your risk. Not bad.

But here’s the twist: what if Centum gaps down to KES 16 overnight? Your stop at KES 17.21 gets hit at KES 16, and you lose KES 7,500—1.5x your planned risk. That’s slippage, and it’s why you should always size your positions conservatively on the NSE. The market doesn’t care about your plans.

Common Mistakes

Mistake 1: Ignoring the stop-loss. You buy KCB at KES 45 with a stop at KES 42, but when it hits KES 43, you move your stop to KES 41 “just to give it room.” Next thing you know, it’s at KES 38, and you’ve lost 15%. Position sizing only works if you honor your stops. The NSE’s volatility means your stop is your best friend—or your worst enemy if you ignore it.

Mistake 2: Overestimating liquidity. You see I&M Holdings at KES 30 and think, “I’ll buy 10,000 shares—easy exit.” But when you try to sell, the bid-ask spread is KES 0.50, and you only get filled at KES 29.50. Your 10,000 shares cost you KES 5,000 in slippage. Always check the daily turnover before sizing a position. If the stock trades less than KES 50 million a day, halve your position size.

Mistake 3: Chasing yield without risk management. You buy Bamburi Cement at KES 120 because the dividend yield is 8%. But the stock’s beta is 1.4, meaning it drops 14% when the market falls 10%. You size your position like it’s a utility stock, but when the market corrects, you’re down 20% before the dividend is even declared. Position sizing isn’t just about the upside—it’s about surviving the downside.

Mistake 4: Using the same size for every trade. You risk 2% on Safaricom (liquid, stable) and 2% on Car & General (illiquid, volatile). That’s like using a sledgehammer to crack a peanut. The NSE’s small-cap stocks can move 20% in a day based on a rumor. Size your positions inversely to volatility—bigger for stable stocks, smaller for wildcards.

Checklist

• Verify your stop-loss. Before you buy, ask: What price will prove me wrong? Set it, forget it, and let the math do the work.
• Check liquidity. Look at the stock’s average daily turnover. If it’s less than KES 100 million, consider halving your position size.
• Adjust for volatility. High-beta stocks (like Centum or Nation Media) need smaller positions. Low-beta stocks (like KCB or Safaricom) can handle larger sizes.
• Review your portfolio risk. If one stock (say, Safaricom) makes up 30% of your portfolio, you’re not diversified—you’re gambling. Rebalance to ensure no single position risks more than 5% of your total capital.

Concept

Break this concept down so a 5-year-old (or a distracted adult) can understand it. Use an analogy. Make it foundational but fun.

NSE Context

Why does this matter on the Nairobi Securities Exchange? Explain how things like liquidity constraints or local banking dominance change the rules here.

Practical Example

Walk through a numerical example using realistic NSE figures, but keep it breezy and easy to follow. Show them why this number matters.

Common Mistakes

• Treating a single metric as gospel without checking the whole picture.
• Ignoring the harsh reality of liquidity constraints when sizing up positions.
• blindly applying Wall Street theories without adapting to the Kenyan risk premium.

Checklist

• Define your thesis and invalidation point before jumping in.
• Respect your account-level risk limits.
• Always verify the filing data before buying into the hype.

Informational only, not investment advice.